The Real Alien Threat (Apocalypse)

Finally, the big picture, though if you've been reading your biochemistry research reports carefully you've probably already guessed it. Micronoids are intelligent psionic micro-organisms that live in the bloodstream of a host body and control it psionically, and they are the true masters of the alien forces. This finally explains how brainsuckers work, how the aliens are able to gain control of human organisations and why the aliens are invading in the first place when their physiology is incompatible with our dimension. This research topic allows for the research of Toxin C, the most POWERFUL toxin in the game! Yes! This is exactly what you've all been waiting for... except that you have to research EVERYTHING in order to get it, just short of the Queenspawn and the Overspawn.

Official Entry: "It is now clear to us that the Micronoid organisms are the source of the Alien intelligence and they are using the various Alien forms to initiate an assault on our dimension. The large Alien life forms cannot survive in our dimension - the Micronoids must transfer to a new host in order to conquer our world and the ideal host is our own race. Brainsuckers are used to introduce Micronoids into the human bloodstream which then gain control of the brain and have access to all the knowledge and abilities of the host. We now understand the physiology of the Micronoids sufficiently in order to develop a specific toxin that will kill the organisms in the bloodstream."

This information is somewhat at odds with the game over cinematic that shows the earth being engulfed in explosions and then teleported away.

While the research text says that Toxin C is effective against Micronoids in the bloodstream, it is not effective against brainsucked XCOM agents.